Low Magnesium Level

[aramis]

First off, my tank (RSM 250) is about three months old, and currently FOWLR. Recent water testing has shown my magnesium level dropping (it was 1080), as well as my calcium (380) - these used to be > 1250 and 450 respectively - my alk is OK, at 9.15. I was wondering, since I don't yet have any corals, is there a reason why my mag and calc are dropping? I'm using Red Sea Coral Pro which advertises higher readings than what I'm getting. BTW, I religiously do weekly water changes of ~ 8 gallons which I thought would replentish these elements to desired levels. I'm using Salifer test kits and they recommend using Salifert Magnesium if levels are less than 1200 but I don't want to do that without first trying to understand what's causing the drop. Could it be that I have a sub-par batch of salt or are these just steady state values now that my tank is becoming more established and I need additives to keep things in check? Any thoughts or suggestions greatly appreciated.

 

[Reefmack]

Hi aramis. Have you tested your mixed SW for Ca, Alk, and Mg? That might be a good place to start. pH of the tank? Ca ang Mg are closely related, as is the effect of the Alk. I can't explain the drops, but a post in the chemistry forum might get you some good information.

Maybe this link will help too:

Reef Aquarium Water Parameters by Randy Holmes-Farley - Reefkeeping.com

 

[aramis]

Hey Reefmack - it dawned on me after I posted (I hate when that happens) that I should test my pre-tank mix. I have 16 gallons already made in advance of my next water change. I'll test that when I get home tonight. Good catch - my pH is OK too - around 8.2. Thanks for the suggestions and the link!

 

[Reefmack]

OK - let us know what you find with the tests on the SW. I've noticed that after my SW ages a week that after reheating, stirring and aerating the second time a week later, my pH drops from 8.1-8.2 to about 7.8-7.9. I add a pH buffer to get it back up before using it. It may have nothing to do with what's going on but I thought I'd mention it. To be honest I haven't checked anything but Ca recently on my fresh SW, and when I last did my Ca on the RS Coral Pro was about 490 - higher than I expected.

 

[aramis]

Interesting - I've only checked that my temp and salinity are spot on before adding my aged s/w to the tank - this batch was made last Saturday so I'll test tonight then post my results. BTW, maybe you've seen this but I thought I'd add it here just in case:

http://aquariumwatertesting.com/AWT_Salt_Analysis_0208.pdf

Any idea why there's two 'Red Sea Coral Pro' samples in each test? Funny though, the one sample shows values really close to the calc and mag that I'm getting.

 

[Reefmack]

I've always like the AWT test results, but they're flawed in one respect. At the beginning the salinities at 7.0 g/200 ml. were found to vary a lot between salts, yet this doesn't appear to have been adjusted for in the following tests, which were all run at the same 7g/200ml. So a salt that had a higher salinity would have less of it used when we make up SW, and that should have been taken into account. A salt with high salinity would actually have lower amounts of the other parameters. I think 2 tests were run on some of the salts to maybe get a picture of the variance between different batches?

 

[VP Clown]

How do measure your salinity is it refractometer, recommended, or hydrometer.
If making small batches like we do for red sea max, do you give the bucket of salt a good shake around as it is known that different elements settle tothe bottom of the bucket.
As you Ca and Mg results are both low it could be that you are making up a bit weak, do you weigh or measure the salt.
There was a big debate on a UK forum about a certain salt and it turned out that it was made up a bit on the light side, not much either, i'll see if i can find the numbers

This was posted in the uK forum from one of the owners, I think, of D&D when the results of their salts was questioned
Seems to be a logical approach

1 - Recalibrate the refractometer with the instrument at 20C
2 - Adjust the salinity to 35.5ppt on the right hand scale - about 1.027 on the salinity scale - if you are looking for 1.025 on your refractometer then the salinity could be down by 7% - ie 1283 rather than 1380.

3 - Measure the calcium with a reliable test kit - salifert or Tropic Marine Calcium/Magnesium test (be careful as the chart on the card and in the instructions varies by 100ppm)

4 - Measure the magnesium ideally with the Tropic Marine Calcium/Magnesium test kit - We say this as we have extensively tested many magnesium kits on the market and many common tests were found to be out by 10%, ie a reading of 1242 rather than 1380 could still be correct.
If you combine this with a salinity error then you could be down by 7% and 10% - 1155

HTH Andy

 

[aramis]

Andy:
- I measure my salinity with a refractometer
- I haven't shaken the bucket prior to using; just scoop off of the top (I'd never heard anyone say to do that - good suggestion though)
- I normally make about 16 gallons a week out, with an set weight of salt getting me very close to my desired salinity (1.023) and keep it heated so it's ready to go whenever I need it

Red Sea Coral Pro advertises something like 450 calc with each batch, but I did my water testing only two days after my last water change and I was getting a reading as I stated above around 380; when I also saw the low mag level I became curious as to what the problem might be (especially since I don't have any corals yet).

Thanks for the reply!

 

[Reefmack]

VP Clown - good and interesting information on the Tropic Marine Calcium/Magnesium test kit being most accurate.

 

[VP Clown]

Andy:
- I measure my salinity with a refractometer
- I haven't shaken the bucket prior to using; just scoop off of the top (I'd never heard anyone say to do that - good suggestion though)
- I normally make about 16 gallons a week out, with an set weight of salt getting me very close to my desired salinity (1.023) and keep it heated so it's ready to go whenever I need it

Red Sea Coral Pro advertises something like 450 calc with each batch, but I did my water testing only two days after my last water change and I was getting a reading as I stated above around 380; when I also saw the low mag level I became curious as to what the problem might be (especially since I don't have any corals yet).

Thanks for the reply!

It is recommended to mix your bucket well, I really prefer to use the small buckets as i find those easier to mix up. Some people supposedly kick them around the garage for a while, some lfs's gve out empty buckets so you can mix it by pouring between the two. DD actually now recommend it on the leaflet in the bucket.

I think the fact you make your salinity is a little on the low side that this will give you lower mag and ca results.
Red Sea coral Pro do advertise 450 calc at 1.023, but I always mixed mine to 1.026, 35.5ppt on refractometer and never had any calc issues, I've since switched to DD H20 and they recomend 35.5ppt to get there levels -I have heard these salts are all the same - I suppose this shows they may not be?

Another quote from them was that Calc and Mag are two of the biggest elements that are in your salt so if there wrong then what chance have they got with the small elements ie strontium and the like

Andy

 

[aramis]

Thanks for all of the info Andy. I tested my pre-tank batch last night and I received the same readings - so it looks like my tank is at equilibrium with any new water that I add - at least for mag and calc. I still had the Red Sea Test kits from when I bought the tank so I tested mag + calc and their readings were also low (even a little lower than my Salifer results). I will re-calibrate my refractometer tonight and see if my salinity readings might be contributing to the low levels and mix the remaining salt in my bucket as you suggested above. Then I'll make a small batch and re-test to see if that was the problem. BTW, since my tank is currently FOWLR do you think these low levels are a concern? Obviously I want to get my levels up to optimal, but at the same time, if there is no harm to my fish, I'd like to finish this bucket of salt (175 lbs). Also, I assume it would be best to first raise my mag levels before concentrating on my calc? I have a container of Seachem Reef Advantage Calcium which will also raise mag but only at a 100:5 ratio. I don't want to waste this if the low mag levels will continue to drag my calc down. Finally, I've read Epsom Salts has been used to raise mag levels. Could I use this first to get my mag levels optimal then switch to the Reef Advantage to get my calc up?

 

[mbdave]

Is your alk reading in KH or mls? If its mls thats high and your calcium and mag will read low, do you add buffer to raise alk? If so this will cause a low cal and mag reading. Also I use IO salt and its always low in mag and calcium "at least when I have tested it". I saw it mentioned in here to about bubbling salt after it sat for a few days if I'm not mistaken my reference is not in front of me" but that might drop your ph a little "I could be backwards and its suppose to raise it a little" what ever leaving it in the dark could lower it.... What I'm gettign at is in a FO tank I would not sweat it unles you are trying to get your coraline or something going..
Good Luck,
Dave

 

[aramis]

Hey Dave - if I remember correctly my alk reading was 3.25 meg/l which I thought converted to the 9.15 dKH. I have yet to put any additives into my tank since set up (about 3 months ago), and I've been using Red Sea Coral Pro salt throughout. Therefore, all of my readings are a direct result of the salt - I think my alk has always been around 9 - thought that value was OK. You did bring up another point that interests me - I've been making up a batch of water ~ 1 week in advance of my next water change. In addition to a heater, I have the RSM stock skimmer pump in the container constantly circulating the water. I've read this is the way to go, but not sure if it's entirely necessary. Between the tank and sump downstairs and this container constantly percolating upstairs I feel like I'm living under water. Plus I'll never be able to tell if I've ever left a faucet on accidentally!

 

[aramis]

Oh - forgot to mention that I do want to add corals eventually but not until I understand what's going on with my lower than usual mag and calc readings first. Just taking it slow ...

 

[mbdave]

Yeah 9+ is Ok for me I would verify my test kits are good and add mag. You can get epsoms salt and make a mag mix pretty easy and cheap.
Also I use a powerhead to stir the water also works fine but in most cases I also use the water within 48 hours.

 

[VP Clown]

I would deffo just try and make a batch up to 1.026 and test and see if the mag and calc are at a desirable level before adding extras, its easier and cheaper if you can get the mix up to correct levels by sg that adding to get correct, you start to depend on notoriously unreliable test kits when you do this, IMO even the best test kits are only a guide

You shouldn't be using much mag and calc up on a FOWLR unless your producing lots of corraline and even then you should be able to keep up with regular water changes

Andy